The reception of global positioning system (GPS) satellite position data may be problematic and may negatively impact the performance of GPS receiver. The conventional approach to using global positioning system (GPS) satellites to determine a receiver's position requires the receiver to download navigation messages from four or more visible satellites, extract the broadcast ephemerides for each satellite from the navigation messages, and utilize this ephemeris data to compute the position of the satellites in the ECEF (earth-centered earth-fixed) coordinate system at a specific time. The broadcast ephemerides for each satellite are provided in a frame of data that takes about 30 seconds to send/receive. The broadcast ephemerides are valid for a period of four hours starting from the time the satellite starts to broadcast the navigation data. A control station uploads the data to the satellite less frequently, usually a couple of times a day. After a four-hour period, the receiver has to again download the latest broadcast ephemerides. This process is sometimes referred to a obtaining a “GPS fix”.
Under “warm” or “cold” start conditions, the GPS receiver may not have valid ephemerides, and so it may have to wait until at least four satellites have been acquired and their broadcast ephemerides extracted before estimating a position. This extends the time required to acquire valid ephemerides to beyond 30 seconds, perhaps to several minutes, which may not be acceptable to a user.
Furthermore, under weak signal conditions, the signal-to-noise ratio of the signal from one or more satellites may fall below the receiver's threshold to decode the navigation message. There are other assistance systems such as GSM/CDMA assistance (AGPS/3GPP/3GPPS2) although other assistance schemes require network connectivity, and the components may be expensive.
Hence, two perennial problems with GPS receivers are obtaining an estimate of the current location, and obtaining ephemeris and almanac data. Having this data in advance dramatically speeds up the time to obtaining a position fix. It would be beneficial to have a system and method that provides an alternative procedure to update the current location estimate, ephemeris and almanac data in a GPS receiver.